RT Journal Article SR Electronic T1 Effects of caffeine on anterior pituitary and thyroid function in the rat. JF Journal of Pharmacology and Experimental Therapeutics JO J Pharmacol Exp Ther FD American Society for Pharmacology and Experimental Therapeutics SP 58 OP 62 VO 214 IS 1 A1 Spindel, E A1 Arnold, M A1 Cusack, B A1 Wurtman, R J YR 1980 UL http://jpet.aspetjournals.org/content/214/1/58.abstract AB We studied the effects of acute, intraperitoneal administration of caffeine on serum thyrotropin (TSH), growth hormone, prolactin, thyroxine and 3,3',5-triiodothyronine in rats. Caffeine lowered serum TSH and GH in a dose-dependent manner with ED50 values of 30 and approximately 50 mg/kg, respectively. TSH levels were depressed 1 to 6 hr after injection and correlated with serum caffeine levels greater than 20 micrograms/ml. The decrease in serum TSH was followed by decreases in serum 3,3',5-triiodothyroxine and thyroxine 4 hr after caffeine administration. Theophylline and theobromine had effects similar to those of caffeine on hormone levels. Caffeine did not significantly affect hormone secretion when incubated directly with rat pituitaries in vitro. Administration of antisomatostatin antiserum to rats blocked the inhibitory effects of caffeine on serum GH levels, suggesting that caffeine inhibits GH and TSH secretion by releasing hypothalamic somatostatin.